What is missing is that my partner should have taken this ball as a high BH volley or a FH overhead or volley. As you say, if the ball was actually headed toward me for a FH swinging volley, I would have no need to wind up behind my partner. Which tells you this ball should have been handled by the deuce court player.

If the net player lays off a ball she really should take -- and let's face it, this happens -- then she needs to be alert to get out of the way.

No, I had to go behind her to play the ball. She is middle of service box, I am in no man's land behind her.

These answers are reasonable... for a ball struck to your partner, thus if you take it, you are ending up well beyond the midline. Perhaps your original description of the shot being "up the middle" (neither to your partner, nor to you) is not accurate.

If the shot is in fact midway between you two, the answer to who should take it lies in the relative strengths of your two shots: BH overhead vs FH swinging volley and the location on the other side from where the ball originated, so if the ball was struck from the ad alley it is your shot (all other issues being equal).

BTW if the ball is actually struck to her, props to you for even getting your racquet on it as that is quite a distance to cover.